This invention relates to a tire pressure control system and method, and more particularly, to such a system which includes a pneumatic control unit, a pressure sensor, a rotary seal associated with a tire and a wheel valve rotating with the tire which can be moved into various positions. The system is connected to a source of air pressure. The control unit is connected through a connecting line and the rotary seal is connected to the wheel valve, each of whose positions is a function of the pressure level in the connecting line.
Tire pressure is regulated in agricultural vehicles such as, tractors, to conform to the particular operating condition of the moment. Tractors are increasing in power capability and in total weight. In order to reduce undesirable compacting of the ground, systems for regulating tire pressure can reduce tire pressure during field operation in contrast to the pressure during operation over the road.
EP-B1-0 164 917 shows a central tire inflating system with control devices and a wheel valve. The control devices supply an input pressure for a first connection of a pressure reducing valve. The pressure reducing valve contains a second connection that opens to the atmosphere and a third connection that is connected over a connecting line and a rotary seal with a tire valve rotating with the tire. The first connection and the third connection of the pressure reducing valve are connected to each other when the input pressure exceeds the pressure at the third connection. The third connection is connected to the venting connection when the pressure at the third connection exceeds the input pressure. The wheel valve is connected with a tire that can be inflated. It makes a open possible when a pressure is applied to its input side that exceeds a first reference pressure and when the pressure in the tire lies above a minimum wheel reference pressure. The tire is vented through the pressure relief valve that is located ahead of the rotary seal. For this purpose the system must be pressurized with a venting pressure so that the wheel valve takes on its open position. This venting pressure opposes the actual venting of the pressure chamber which hinders the venting process. Beyond that the venting connection located far ahead of the pressure chamber slows and hinders the venting process.
DE-OS-38 36 105 shows a tire pressure regulating installation for off-road motor vehicles consisting of a stationary valve combination, a rotary seal per wheel for a pressurized air supply line as well as for a control line and a valve combination for each wheel rotating with the wheel. The stationary valve combination includes a relay valve, at least one pilot valve and a closing pressure control valve. The valve combination rotating with the wheel includes a wheel control valve which is opened by a pressure impulse from the supply line and is closed by the control pressure in the control line, and a quick release valve located ahead of it which is used for the venting of the tire pressure. A check valve may follow the venting opening of the quick release valve. In this configuration the control line as well as the supply line must be connected through a rotary seal with the wheel control valve. This is costly and expensive.